Microbes and food spoilage — A/L Biology

What must I remember about Microbes and food spoilage?

• Food spoilage is the sensory, biochemical, and nutritional deterioration of food rendering it unpalatable or unsafe for human consumption, driven primarily by microbial proliferation and endogenous tissue autolytic enzymes.
• Microbial groups responsible for food deterioration: Molds (Aspergillus, Penicillium, Rhizopus causing fungal rot on bread/fruits), Yeasts (fermenting fruit juices producing off-flavors and gas), and Bacteria (Pseudomonas spoiling chilled meat/milk, lactic acid bacteria souring wines, spore-formers Bacillus and Clostridium spoiling canned/cooked foods).
• Foodborne infections vs Foodborne intoxications: Foodborne infection results from ingesting living viable pathogens that colonize gut epithelium (e.g., Salmonella enterica, Campylobacter jejuni, Listeria monocytogenes); Foodborne intoxication results from ingesting pre-formed microbial toxins in food without requiring live microbe ingestion (e.g., Staphylococcus aureus enterotoxins, Clostridium botulinum botulinum neurotoxin).
• Mycotoxins and fungal carcinogens: Toxic secondary fungal metabolites produced on crops: Aflatoxins (synthesized by Aspergillus flavus and Aspergillus parasiticus on improperly stored peanuts, maize, chili; potent hepatotoxins causing cirrhosis and hepatocellular carcinoma).
• Food hygiene and HACCP: Hazard Analysis and Critical Control Points (HACCP) is a systematic preventative management system identifying biological, chemical, and physical hazards along food supply chains (farm to fork) to implement verified critical control thresholds.

Test yourself (1 minute)

1. Clostridium botulinum neurotoxin hazard

   Obligate anaerobic spore-former producing botulinum toxin (lethal dose < 1 μg), blocking acetylcholine release at neuromuscular junctions causing flaccid paralysis; prevented by commercial pressure canning at 121°C ('botulinum cook') to sterilize endospores.

2. Danger Zone for food storage

   The temperature range between 5°C and 60°C (41°F - 140°F) allows exponential bacterial replication; hot foods must be kept >60°C and cold foods <5°C to arrest microbial division.

3. Staphylococcal enterotoxin heat-stability

   Staphylococcus aureus enterotoxin A is remarkably heat-stable, withstanding 100°C boiling for 30 minutes; boiling spoilt custard or cream cakes kills vegetative bacteria but leaves the enterotoxin fully intact to cause explosive vomiting and diarrhea.

Practise Microbes and food spoilage questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 9

What should I study first?

What comes next?

Next in the syllabus

Where does Microbes and food spoilage fit in the syllabus?

Year 2 · Term 3